Dopamine neurons in the VTA play a very important role in a variety of physiological as well as addictive behaviors. The main goal of the present proposal is to elucidate the relationship between plasticity at excitatory synapses in the ventral tegmental area (VTA)and addictive behaviors such as behavioral sensitization and self-administration of cocaine. During the current funding period (April1st, 2002- February 2006), we have collected evidence that might explain the sequence of events leading from NMDAR activation in the VTA produced by acute cocaine application, to long-term potentiation of VTA neurons that results as a consequence of in vivo cocaine exposure. Further, our preliminary data suggest that long-term changes of excitatory synaptic transmission in the VTA are not only produced by passive cocaine administration (e.g.in vivo cocaine injections), but operant behaviors such as cocaine self-administration. Specific aim 1 will test the hypothesis that in vivo cocaine-induced potentiation involves a direct action of cocaine in the VTA mediated by NMDARs, D5 receptors and the cAMP/PKA-dependent pathway. Specific aim 2 will test the role and time-course of protein synthesis in mediating long-term plasticity at VTA synapses and behavioral sensitization. Finally, specific aim 3 will characterize whether long-term synaptic changes at glutamatergic synapses in the VTA are produced during forced abstinence or extinction of operant responding from either food or cocaine. Taken together, the results from these experiments will likely help us understand the role of plasticity at glutamatergic synapses in the VTA in mediating cocaine-dependent behaviors.